1. Field of the Invention
The present invention is related to a feedthrough capacitor and a magnetron using this feedthrough capacitor.
2. Description of the Related Art
Referring now to FIG. 6 to FIG. 8, this sort of conventional feedthrough capacitor will be described. FIG. 6 is a sectional view for showing a conventional feedthrough capacitor equipped with a ceramic capacitor. FIG. 7 is a partially sectional view for representing a magnetron equipped with the feedthrough capacitor. FIG. 8 is a sectional view for indicating a conventional feedthrough capacitor which does not contain a ceramic capacitor.
The conventional feedthrough capacitor 1 shown in FIG. 6 has been equipped with two through holes 2 which are separately arranged in an interval, and an electrode 3a and another electrode 3b which are independently provided from each other on one plane of each of the through holes 2. A portion of a common electrode 4 of a ceramic capacitor 5 which owns the common electrode 4 has been fixed on a floating portion 8 of an earth metal fitting 7 having a through hole 6 by way of a soldering work, or the like. Two feedthrough conductors 11 have penetrated the independent electrodes 3a and 3b, while these two feedthrough conductors 11 own electrode connecting portions 9a and 9b, and have been covered with insulating tubes 10. The electrode connecting portions 9a and 9b have been fixed to the electrodes 3a and 3b by way of a soldering work, or the like, respectively. Then, an insulating case 12 has been mounted in such a manner that the floating portion 8 of the earth metal fitting 7 and the ceramic capacitor 5 are surrounded by an insulating cover 13. An insulating resin 14 such as an epoxy resin has been filled into a peripheral portion of the ceramic capacitor 5 which has been surrounded by both the insulating case 12 and the insulating cover 13. A terminal portion 11a of the above-explained feedthrough conductor 11 has constituted a terminal for connecting a wiring line, and the like.
As indicated in FIG. 7, the feedthrough capacitor 1 constructed in the above-described manner has been mounted on a side surface of a filter case 16 of the magnetron 15 and has been fixed, and an inductor 19 has been series-connected between a cathode terminal 18 of a cathode stem 17 and the feedthrough conductor 11 of the feedthrough capacitor 1 so as to be employed as a filter circuit of a power input unit of the magnetron 15.
However, since the feedthrough capacitor having the above-explained structure employs the ceramic capacitor, the following problems may occur:
(1) The soldering work, or the like must be carried out in order to connect the electrode portion, so that a heat resisting temperature is adversely influenced by a melting point of a solder, or the like.
(2) The insulating resin must be filled in order to secure a moisture resistance property and an insulating property. Since the thermal expansion coefficient of the insulating resin is different from that of the ceramic capacitor, peeling may occur on the contact planes between the insulating resin and the ceramic capacitor, so that a voltage withstanding failure may occur. It is practically difficult that the ceramic capacitor adheres to the insulating resin in such a manner that the peeling does not occur.
(3) While the cost of the ceramic capacitor is high, the assembling method cannot be simplified since the high assembling precision is required, so that higher cost is required.
In order to solve the above-described problems, such feedthrough capacitors which do not contain ceramic capacitors have been conceived (refer to, for example, Japanese Utility Model Application No. Hei-1-135725).
A feedthrough capacitor 20 shown in FIG. 8 has been provided with flat plate-shaped inner conductors 21a and 21b which are arranged parallel to each other; an outer conductor 22a having an elongated cylindrical shape which is arranged close to the inner conductor 21a in such a manner that the inner conductor 21a is surrounded by the outer conductor 22a; an outer conductor 22b having an elongated cylindrical shape which is arranged close to the inner conductor 21b in such a manner that the inner conductor 21b is surrounded by the outer conductor 22b; and a flange 23 formed with the outer conductors 22a and 22b in an integral body. All of these structural members have been molded in an integral body by employing either a thermosetting resin, or a thermoplastic resin, otherwise, such an insulating resin 24 which is manufactured by mixing dielectric ceramic powder with these resins. Also, the insulating resin 24 has been filled into a space between the inner conductor 21a and the outer conductor 22a, and another space between the inner conductor 21b and the outer conductor 22b. Thus, a capacitance has been produced between the inner conductor 21a and the outer conductor 22a, and another capacitance has been produced between the inner conductor 21b and the outer conductor 22b (refer to, for example, Japanese Utility Model Application No Hei-76432).
However, in the above-explained conventional feedthrough capacitor without containing the ceramic capacitor, the below-mentioned problems occur. That is, when the molding work is carried out by employing the insulating resin, the relative position between the feedthrough conductor and the earth metal fitting is shifted, and the insulating resin is insufficiently filled to produce an air gap. As a result, a voltage withstanding failure may occur. Also, the ceramic powder contained in the insulating resin is clustered on one side of the insulating resin while the insulating resin is being hardened, so that performance of the capacitors may be fluctuated.